<h4>Tool</h4><table border="0"><tr><td valign="top"><b>Name</b></td><td valign="top">Multi Direction Lee Filter</td></tr><tr><td valign="top"><b>ID</b></td><td valign="top">3</td></tr><tr><td valign="top"><b>Author</b></td><td valign="top">Copyrights (c) 2003 by Andre Ringeler</td></tr><tr><td valign="top"><b>Specification</b></td><td valign="top">grid</td></tr></table><hr><h4>Description</h4>The tool searches for the minimum variance within 16 directions and applies a Lee Filter in the direction of minimum variance. The filter is edge-preserving and can be used to remove speckle noise from SAR images or to smooth DTMs. Applied to DTMs, this filter will preserve slope breaks and narrow valleys.

For more details, please refer to:
Lee, J.S. (1980): Digital image enhancement and noise filtering by use of local statistics. IEEE Transactions on Pattern Analysis and Machine Intelligence, PAMI-2: 165-168

Lee, J.S., Papathanassiou, K.P., Ainsworth, T.L., Grunes, M.R., Reigber, A. (1998): A New Technique for Noise Filtering of SAR Interferometric Phase Images. IEEE Transactions on Geosciences and Remote Sensing 36(5): 1456-1465.

Selige, T., Böhner, J., Ringeler, A. (2006): Processing of SRTM X-SAR Data to correct interferometric elevation models for land surface process applications. In: Böhner, J., McCloy, K.R., Strobl, J. [Eds.]: SAGA - Analysis and Modelling Applications. Göttinger Geographische Abhandlungen, Vol. 115: 97-104 <a href="http://downloads.sourceforge.net/saga-gis/gga115_09.pdf">&lt;PDF&gt;</a>


<hr><h4>Parameters</h4><table border="1" width="100%" valign="top" cellpadding="5" rules="all"><tr><th>Name</th><th>Type</th><th>Identifier</th><th>Description</th><th>Constraints</th></tr>
<tr><th colspan="5">Input</th></tr><tr><td>Grid </td><td>Grid (input)</td><td>INPUT</td><td></td><td></td></tr><tr><th colspan="5">Output</th></tr><tr><td>Filtered Grid</td><td>Grid (output)</td><td>RESULT</td><td></td><td></td></tr><tr><td>Minimum Standard Deviation (*)</td><td>Grid (optional output)</td><td>STDDEV</td><td></td><td></td></tr><tr><td>Direction of Minimum Standard Deviation (*)</td><td>Grid (optional output)</td><td>DIR</td><td></td><td></td></tr><tr><th colspan="5">Options</th></tr><tr><td>Estimated Noise (absolute)</td><td>Floating point</td><td>NOISE_ABS</td><td>Estimated noise in units of input data</td><td>Default: 1.000000</td></tr><tr><td>Estimated Noise (relative)</td><td>Floating point</td><td>NOISE_REL</td><td>Estimated noise relative to mean standard deviation</td><td>Default: 1.000000</td></tr><tr><td>Weighted</td><td>Boolean</td><td>WEIGHTED</td><td></td><td>Default: 1</td></tr><tr><td>Method</td><td>Choice</td><td>METHOD</td><td></td><td>Available Choices:
[0] noise variance given as absolute value
[1] noise variance given relative to mean standard deviation
[2] original calculation (Ringeler)
Default: 1</td></tr></table>(*) <i>optional</i>